The present invention relates in general to fluid flowmeters and in particular to a new and useful vortex shedding flowmeter having an easily replaceable sensor assembly.
When a non-streamlined body is placed in a stream of moving fluid, layers of slow moving fluid are formed along the outer surface of the body and are shed in the form of repeating vortices. In a uniform flow of fluid, the frequency of these vortices is related in a linear way to the fluid velocity.
Flowmeters which take advantage of the vortex shedding phenomenon are known, for example from U.S. Pat. No. 4,171,643 to Frick. This reference shows the use of a strain gage for sensing the passage of vortices. The strain gage is mounted on a sensor assembly which can be replaced.
U.S. Pat. No. 4,519,259 to Pitt et al discloses a vortex shedding flowmeter which utilizes a light barrier to sense the passage of a vortex.
Various vortex shedding flowmeters are commercially available from companies such as Yokogawa, Foxboro, and Fisher & Porter. None of these available products, however, have in-line replaceable sensors in that the sensors of these products cannot be replaced without interrupting or diverting to a bypass pipeline the flow being measured. Most manufacturers utilize some type of electric sensors such as a piezoelectric sensor or stain gage. These sensors are permanently installed in the sensing device, usually by welding. Because of this the entire device must be replaced if failure occurs in the sensor, during manufacturing or operation.
Failure of the sensing element during operation requires a shutdown in the process being measured or a bypass line and valves must be in place if interruption of the process is undesirable. In both cases large costs are incurred. This is required since it is necessary to disturb the pressure boundary in the process in order to replace the sensing element.